The present invention concerns a method of producing a double chamber container for a pressure-valve can which is usable for dispensing flowable products, in particular products containing solvents or products for the cosmetics industry, having a single or multiple part metallic outer container and a compressible metallic inner container, as well as a double chamber container produced according to this method and its use in pressure-valve cans.
Such double chamber containers are found in about 2% of the approx. 6 billion spray cans used worldwide and have proven their worth in particular for the storage and dispensing of the most various types of products. Cans in which the propellant is separated from the filler product, hereinafter called double chamber cans, are of increasing importance; on the one hand, because the propellant used in such cans and which is usually flammable, such as butane, propane etc., is retained in the double chamber container and can be disposed of in a controlled manner, and on the other hand, because such cans permit the use of compressed gases, in particular air, nitrogen, carbon dioxide etc., which would chemically alter the filled products if these came into contact with the propellant.
Metallic containers, in particular those made of aluminium, are particularly suitable for the manufacture of such double chamber cans and are known, for example, from DE-38'08'438 or EP-017'147. These double chamber cans either have a plurality of parts, i.e. they comprise a rigid cylindrical casing part, a bottom part, a container lid (dome) and a flexible, metallic inner container, or they are made as two-part containers, i.e. they comprise a one-piece tapering outer container and a flexible, metallic inner container. These types of cans have a variety of technical drawbacks. Thus, when using different metals such as, for example, tinplate combined with aluminium, undesired bimetallic effects can occur at the seams which require special treatment. In other cases the adhesives used are not universally suitable for all types of filler products, therefore requiring an additional protective coating between the adhesive and the filler product. Last but not least, soldering or other types of bonding methods can lead to undesired deformations and weakened points in container parts which have been manufactured as thinly as possible, and thus do not fulfill the high standards set for pressure resistance.
Small containers are known in which a cylindrically formed inner container is inserted from above into a cylindrical outer container. These containers are sealed with conventional valves and therefore have an inner diameter of approx. 25.4 mm (1 inch). With this type of construction it is possible to manufacture containers having a filling capacity of 15-70 ml; however, this type of construction is not suitable for providing commercial pressure-valve cans having a filling capacity of commonly 70-250 ml or more because the intermediate space provided for the propellant between the outer container and inner container may not amount to more than 40% of the volume of the outer container, this standard varying from country to country. For example, under optimal conditions it is only possible to acheive a ratio of filling capacity to intermediate space volume of 45:55 by means of a cylindrical inner container having 80 ml filling capacity which has been inserted into an outer container whose aperture has a conventional valve closure of 1 inch diameter, this tapering outer container being 40.times.170.5 mm large and having a filling capacity of 175 ml. The only admissible ratio of 60:40 cannot therefore be reached with this type of construction.
This prior art makes it clear that the known methods of pressure proof fixation of the metallic inner container to the outer container are either technically complex (gluing and coating), can lead to insufficiently safe cans (weak points), or these cans are not suitable for large volume or true filling (waste of material, cheat packaging).